Electromagnetic actuators

ABSTRACT

A valve comprises an electromagnetic actuator including a solenoid. The solenoid includes at least one core and an anchor plate. The solenoid further comprises at least one coil disposed within the core and connected to a set of power electronics to supply current to the coils. The actuator further comprises a plunger connected to the anchor plate and at least one spring configured to guide the plunger. The actuator also includes a pressure compensation system. The opening and closing of the valve is controlled by passing current through the coil.

BACKGROUND OF THE INVENTION

The invention relates generally to electromagnetic valve actuators forcontrolling valve operation. More particularly, the invention relates toelectromagnetic actuators for controlling valve timing in compressors.

One technique to control the load of large compressors is to activelycontrol the opening time of the suction valves of the compressor. Whenthe load on the compressor is low, the suction valves are kept open fora longer period of time compared to compressors handling higher loads.Typically for a no-load condition, the suction valves of the compressorare kept open for the entire period of operation. In a reversesituation, for a full load condition, the suction valves operate withoutany active control on the opening and closing of the valves.

Currently, either pneumatic or hydraulic actuators establish activecontrol of opening time of the suction valve. Both techniques need aseparate supply of hydraulic/gas pressure and oil/gas pressure pipes toconnect each actuator to the supply system, which supply system isexpensive and has to be maintained regularly. Furthermore, pneumaticactuators cannot achieve high actuation speed and may not be suitable tobe used for continuous control of valve position in each compressioncycle.

Therefore there is a need for an efficient, inexpensive and lowmaintenance actuator for controlling the valves in a compressor.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a valve comprises an electromagnetic actuator including asolenoid. The solenoid includes at least one core and an anchor plate.The solenoid further comprises at least one coil disposed within thecore and connected to a set of power electronics to supply current tothe coils. The actuator further comprises a plunger connected to theanchor plate and at least one spring configured to guide the plunger.The actuator also includes a pressure compensation system. The openingand closing of the valve is controlled by passing current through thecoil.

In another aspect, a valve comprises an electromagnetic actuatorincluding a solenoid. The solenoid includes at least one core, whereinthe core is an “E” shaped core or a “U” shaped core and an anchor plate.The solenoid further comprises at least one coil disposed within thecore and connected to a set of power electronics to supply current tothe coils. The actuator further comprises a plunger connected to theanchor plate and at least one spring configured to guide the plunger.The actuator also includes a pressure compensation system including apressure compensation chamber to balance a compressed gas force actingon said plunger. The opening and closing of the valve is controlled bypassing current through the coil.

DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein;

FIG. 1 illustrates an exemplary electromagnetic actuator in OFFposition;

FIG. 2 illustrates an exemplary electromagnetic actuator in ON position;

FIG. 3 illustrates an exemplary electromagnetic actuator with platesprings;

FIG. 4 illustrates an exemplary electromagnetic actuator with spikes atthe edge of the core;

FIG. 5 illustrates an exemplary bi-directional electromagnetic actuator;

FIG. 6 illustrates the exemplary bi-directional electromagnetic actuatorof FIG. 5 in “on” position;

FIG. 7 illustrates the exemplary bi-directional electromagnetic actuatorof FIG. 5 in “off” position;

FIG. 8 illustrates another exemplary electromagnetic actuator;

FIG. 9 illustrates an exemplary electromagnetic actuator with a pressurecompensation system;

FIG. 10 illustrates another exemplary electromagnetic actuator with apressure compensation system;

FIG. 11 illustrates yet another exemplary electromagnetic actuator witha pressure compensation system;

FIG. 12 illustrates another exemplary electromagnetic actuator with apressure compensation system;

FIG. 13 illustrates an exemplary electromagnetic actuator with apressure compensation system with an additional spring;

FIG. 14 illustrates an exemplary electromagnetic actuator with a failsafe position of the springs;

FIG. 15 illustrates an exemplary electromagnetic actuator with a failsafe design using an additional lock solenoid;

FIG. 16 illustrates an exemplary electromagnetic actuator with a failsafe design using an additional lock solenoid in closed position;

FIG. 17 illustrates an exemplary electromagnetic actuator with permanentmagnets;

FIG. 18 illustrates another exemplary electromagnetic actuator withpermanent magnets; and

FIG. 19 illustrates an electrical damping method to reduce impact of thesolenoids in a electromagnetic actuator.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 illustrate an exemplary electromagnetic actuator 10,including a solenoid 12 and a plunger 18 disposed within a housing 22.The electromagnetic actuator 10 may be coupled to a valve 40 configuredto move between a closed position (FIG. 1) and an open position (FIG. 2)to prevent or permit flow respectively. The solenoid 12 comprises atleast one core 14, for example, an “E” shaped core or a “U” shaped core.The solenoid 12 also includes an anchor plate 16 and at least one coil26 disposed within the core 14. The coils 26 are connected to a powersupply 36 configured to supply current to the coils 26.

As shown in FIG. 1, the exemplary actuator 10 includes two coils 26disposed within the core 14. The plunger 18 is coupled to the anchorplate 16. The valve 40 comprises a valve seat 37 and a valve closingelement 38. The valve 40 may be kept in an open position by a downwardmovement of the plunger 18 against the valve closing element 38. Themovement of the plunger 18 is controlled by passing current through thecoils 26 within the core 14. In some embodiments, the plunger 18 may becoupled to the closing element 38 to actively open and close the valve40. FIG. 1 illustrates a configuration, in which the power supply 36 tothe coils 26 is switched off and the actuator 10 is in “off” positionwith the valve 40 in a closed position. FIG. 2 illustrates the sameactuator 10 shown in FIG. 1 in an “on” position. In operation, whenelectrical current is supplied to the coils 26, the core 14 generates anelectromagnetic force and the anchor plate 16 is pulled towards the core14 due to this electromagnetic force. As the anchor plate 16 is pulledtowards the core 14, the plunger 18 connected to the anchor plate 16 ispushed downward. As a result of this downward movement (shown by thearrow 34) of the plunger 18, the valve closing element 38 is pushed awayfrom a valve seat 37 and the valve 40 opens. As long as the electricalcurrent is supplied to the coils 26, the electromagnetic force generatedby the core 14 holds the anchor plate 16 close to the core 14, thuskeeping the valve 40 open against the force that is generated by thereverse gas flow 39 through the valve 40.

The actuators discussed herein may be used in valves in a reciprocatingcompressor. In one embodiment, the actuator is used in the suctionvalves of the compressor, to keep the suction valve in an open positionfor a certain period of time. The longer the suction valve is kept in anopen position during the compression stroke, the more gas that is pushedback into the suction line and the less gas that is delivered to thecompressor discharge line. In this way, the amount of gas delivered bythe compressor can be controlled by the opening time of the suctionvalve.

The exemplary actuator 10 as shown in FIGS. 1-2 further includes one ormore springs 20. The springs may comprise, for example, helical or platesprings. As shown in FIGS. 1-2, the actuator 10 include a helical spring20 coupled to the plunger 18 and a wall 30. The wall 30 separates theactuator 10 from a compressor suction zone 32. In operation, the spring20 assists the movement of the plunger 18 by maintaining the plunger 18along a longitudinal axis. When the plunger moves the valve 40 into theopen position (FIG. 2) the spring(s) 20 is compressed. Once theelectromagnetic force is released, the plunger 18 moves the valve 40into a closed position and is assisted in closure by the force generatedby the compressed spring 20.

As discussed in the preceding sections, the shape of the core of theactuators described herein may be, for example, an “E” shape or a “U”shape. To generate a high electromagnetic force in the core in a veryshort span of time, the core of the solenoid as well as the anchor plateare typically manufactured out of metal sheets to avoid eddy currenteffects as eddy current growing in the core may reduce the magnetic fluxproduced by the electromagnetic force. In order to facilitate reasonableease of fabrication of the core out of metal sheets, a suitable designconfiguration should be used. The exemplary “E” shaped or “U” shapedcores described herein can be easily fabricated from metal sheets suchas an iron sheet. Furthermore the “E” shaped core also provides a largearea for the poles developed in the core once the coils are energized.Since the plunger is aligned through the center of the “E” shaped core,the magnetic force generated is distributed uniformly on both sides ofthe plunger (due to the uniform location of the coils 26 with respect tothe center of the “E” core 14) and the movement of the plunger due theelectromagnetic force may be balanced adequately.

FIG. 3 illustrates an exemplary actuator 50 including a plate spring 64.The plate spring 64 includes two arms 52 and 54 attached to the plunger18 through a connection 56. The first arm 52 is coupled at a first end60 to the core 14 and at a second end 56 to the plunger 18. The secondarm 54 is coupled at a first end 58 to the core 14 and at the second end56 to the plunger 18. When the coils 26 are energized, the anchor plate16 is magnetically attracted to the core 14 and the arms 54 and 52 ofthe plate spring 64 are forced into a compressed position as the plunger18 moves downward along path 62. Another function of the plate spring 64is to act as a guide for the plunger 18 and to align the core 14 withthe plunger 18. This alignment is possible as the arms 52 and 54 of theplate spring 64 are uniformly connected to either sides of the core 14.

FIG. 4 illustrates an exemplary electromagnetic actuator 70 furthercomprising spikes 72 at the edge of the core 14. As described above, inoperation, when the electrical supply 36 is turned on, the coils 26 areenergized and the anchor plate 16 is magnetically attracted to the core14. As discussed above, in one embodiment of the instant invention, theelectromagnetic actuator is used in a reciprocating compressor.Typically, the gas force within a compressor would act against themagnetic force of the actuator in several ways. A nearly constant force28 (as shown in FIGS. 1-2) pushes against the valve 40. This constantforce 28 is a result of the pressure differential between the suctionzone 32 and the housing 22. The pressure inside the housing 22 istypically equal to the ambient pressure. The suction zone 32 istypically under an elevated pressure. Additionally, a drag force pullson the valve created from the pressure drop across the valve 40.

In operation, in order to balance the constant gas forces, the core 14of the actuator can be adapted to have a configuration as shown in FIG.4. The spikes 72 on both sides of the core 14 are configured to achievehigher initial forces at the beginning of a stroke to balance theconstant gas force acting on the plunger 18. Accordingly, the holdingforce at the end of the stroke is proportionally reduced. When the coils26 are energized, the magnetic flux developed within the core 14 isguided from the core 14 through the spikes 72 to the anchor plate 16during the initial phase of the stroke as the spikes 72 are closest tothe anchor plate 16. In the compression cycle, closer to the end of thestroke, the main magnetic flux goes through the flat surface 74 of theiron core 14 facing the anchor plate 16 as the air gap between the core14 and the plunger 16 becomes smaller. So at the end of the stroke, whenthe anchor plate 16 is close to the core 14, the magnetic flux generatedfrom the flat surface 74 of the core 14 becomes the main flux to pullthe plunger 18. The magnetic flux guided through the spikes 72 at thisstage does not contribute to holding the anchor plate 16 close to thecore 14. Therefore, in operation, the actuator 70 has a higher initialforce and lower holding force as explained above.

FIGS. 5-7 illustrate an exemplary bi-directional (BDE design)electromagnetic actuator 80. The actuator 80 includes two cores, a firstcore 82 and a second core 84. The cores may be made of iron or any othermetal sheets with good magnetic properties to decrease size and weightof the actuator. In one embodiment, the cores are made of iron-cobaltalloys. The exemplary actuator 80 includes the first core 82 and thesecond core 84 having an “E” shape. In some other embodiments, the coresmay have any other suitable shape including, but not limiting to “U”shape. The actuator 80 further includes a plunger 88 and an anchor plate86 connected to the plunger 88. In some embodiments, the actuator mayinclude four cores. The first core 82 includes a set of two coils 94disposed within the first core 82. The second core 84 includes anotherset of two coils 96 disposed within the second core 84. In someembodiments, the cores may include more than two coils. The actuator 80further includes a first spring 92 and a second spring 90 configured toprovide forward and return forces to assist the movement of plunger 88in both directions. The bi-directional actuator 80 enables the anchorplate 86 to move in forward and backward directions during the operationof the valve 40.

Operationally, the open position 106 of the valve 40 is achieved whenthe current through the coils 96 in the second core 84 is turned on.Once the coils 96 are energized, the plunger 88 is pulled towards thesecond core 84 (shown by arrow 98) thereby compressing the second spring90. This is illustrated in FIG. 6, wherein, the plunger 88 pushes thevalve seat 37 away from the valve closing element 38 to achieve the openposition. Alternatively, the closed position of the valve 40 as shown inFIG. 7 is achieved when the current through the coils 96 is turned offand the current through the coils 94 in the first core 82 is turned on.As a result, the plunger 88 is pushed towards the first core 84 guidedby the first spring 92 (as shown by the arrow 100) and the valve 40closes. The bi-directional design of the actuator may cover longerstrokes compared to the unidirectional designs (as shown in FIGS. 1-4)and provides a higher force during the initial stage of the stroke. Thishigher force is due to the fact that in both the end positions (eithervalve close or valve open) of the stroke, the preloaded compressedsprings 90 or 92 provides a high initial force, which force pushes theplunger 88 and the anchor plate 86 towards the opposite core. Hence thespring force gets added to the weak magnetic forces, present at thebeginning of the stroke due to the large air gap between anchor plate 86and iron cores 82 and 84 and enhances the initial force.

FIG. 8 illustrates another exemplary electromagnetic actuator 110. Theexemplary actuator 110 includes a first core 112 adapted to have spikes124 at both ends of the first core 112. A set of coils 120 are disposedwithin the first core 112 and another set of coils 122 are disposedwithin the second core 114. In operation, once the coils 120 and 122 areenergized, the anchor plate 116 is pulled towards the second core 114and an additional plate 136 coupled to the plunger 118 is pulled towardsthe first core 112 thereby enhancing the downward motion of the plunger118. Due to the spikes 124, the first core 112 may achieve higherinitial forces but low holding force as explained above. As illustratedin FIG. 8, the plot shows the force developed in the actuator 110 whilein operation. The “x” axis or the horizontal axis 128 shows the strokeand the vertical axis or the “y” axis 126 shows the actuator force. Thecurve 132 shows the actuator force developed in the first core 112 withspikes 124. As discussed before, the initial force developed by thefirst core 112 is higher as is evident from the curve 132. The secondcore 114 however has a lower initial force, but a higher holding forceas is evident by the curve 134. The curve 130 projects the behavior ofthe actuator force, which behavior is the sum of the two curves 132 and134. With such a force—stroke characteristics, the constant gas forceacting on the plunger of the actuator may be balanced.

FIGS. 9-13 illustrate exemplary electromagnetic actuators with apressure compensation system, wherein like elements are designated withlike reference numerals. FIG. 9 illustrates an exemplary electromagneticactuator 140 including a pressure compensation system. In thebi-directional designs of actuators as shown in the preceding sections,the gas force permanently acting against the magnetic force developed inthe solenoid can be balanced by proper spring adjustment of both thesprings of the actuator. However in unidirectional designs, in order tobalance the gas force on the solenoid, an exemplary pressurecompensation system is provided as shown in FIG. 9. The actuator 140includes an anchor plate 146 connected to a plunger 152. The actuatorfurther includes a core 142 including two coils 144 disposed in betweenand a spring 154. The actuator 140 is housed in a chamber 148. Thepressure inside the chamber 148 is P₁, which pressure P₁ is typicallyequal to the ambient pressure. The plunger 152 is further connected to awall 178 of a compression chamber 160. The compression chamber 160 is ata pressure P₂, which pressure P₂ is typically higher than the ambientpressure P₁ inside the chamber 148. This higher pressure P₂ in thecompression chamber 160 creates a constant force as shown by the arrow170 acting on the plunger 152. This constant force acting on the plunger152 results in a requirement of a high initial force to move the plunger152 when the electrical energy is supplied to the coils 142. Thepressure compensation system is configured to balance this force 170acting on the plunger 152 to reduce the requirement of a high initialforce at the beginning of a stroke.

In one embodiment, the pressure compensation system includes a firstpressure compensation chamber 156 in fluid communication with thecompression chamber 160 and a second pressure chamber 158 in fluidcommunication with the ambient. The first pressure chamber 156 isconnected to the compression chamber 160 through a first conduit 166.The first conduit 166 is connected to the compression chamber 160through an opening 162 in the wall 178. The second pressure chamber 158is connected to the ambient through the second conduit 168. Inoperation, the gas from the compression chamber 160 at higher pressureP₂ flows to the first pressure chamber 156 and the ambient air atambient pressure P₁ flows to the second pressure chamber 158. Therefore,the force due to the pressure difference (P₂−P₁) acting on the plunger152 in the down ward direction equals the force 170 acting on theplunger 152 in the opposite direction thereby balancing the force 170.The first and second pressure chambers 156 and 158 are separated fromeach other by a seal 174. The second pressure chamber 158 is separatedfrom the compression chamber 160 by a seal 172. The first pressurechamber 156 is separated from the housing 150 by a seal 176. All theseseals are used to prevent mixing of high pressure gas in the compressionchamber 160 with ambient air.

FIG. 10 illustrates yet another exemplary electromagnetic actuator 180including a pressure compensation system. The pressure compensationsystem includes a top pressure chamber 182 disposed on top of thehousing 148. The top pressure chamber 182 is in fluid communication withthe compression chamber 160 through an exemplary plunger 188. Theexemplary plunger 188 is configured to have a hollow passage 190disposed within the plunger 188. The hollow passage 190 connects thecompression chamber 160 with the top pressure chamber 182. In operation,the gas from the compression chamber 160 flows to the top pressurechamber 182 as shown by the arrow 186. Therefore, the pressure insidethe top pressure chamber 182 is equal to pressure P₂ (the pressureinside the compression chamber 160). As a result, an equal force acts onthe plunger 188 from top due to the gas at pressure P₂ in the toppressure chamber 182 and from the bottom due to the same pressure P₂ inthe compression chamber 160. The top pressure chamber 182 is separatedfrom the housing 148 by a seal 184.

FIG. 11 illustrates yet another exemplary electromagnetic actuator 200including a pressure compensation system. The actuator 200 is housed inan exemplary housing 202. The housing 202 includes a bottom portion ofhousing 218 including the anchor plate 146, core 142 and the bottomspring 154. The top portion 216 of the housing 202 includes a step motor212 connected to a top spring 214. The top spring 214 is coupled to theanchor plate 146. The actuator 200 further includes a sensing device 204in fluid communication with the compression chamber 160 to sense thepressure P₂ inside the compression chamber 160. The sensing device isalso connected to a set of control hardware and software 208 connectedto the step motor 212. In operation, the sensing device 204 senses thepressure P₂ inside the compression chamber 160 and sends a signal 206 tothe set of hardware and software 208. The hardware and software 208, inturn, send another signal 210 to the step motor 212 to start building aspring force (F_(spring)) in the top spring 214 which spring force isequal to the gas force 170 (F_(gas)) acting on the plunger 152 from thebottom. In operation, these two equal forces acting in the oppositedirection, F_(spring) and F_(gas) balance each other.

FIG. 12 illustrates yet another exemplary electromagnetic actuator 220including a pressure compensation system. The actuator 220 is housed inan exemplary housing 221. The housing 221 includes a bottom portion ofhousing 224 including an anchor plate 223, the core 142 and the spring154. The top portion 222 of the housing 202 is a pressure compensationchamber connected to an external gas supply chamber 228. The pressurecompensation system further includes a gas supply valve 234 and apressure release valve 236. A gas at high pressure is stored in the gassupply chamber 228. The gas supply chamber 228 is in fluid communicationwith the top portion of the housing 222. In operation, the sensingdevice 204 senses the pressure P₂ inside the compression chamber 160 andsends a signal 238 to a control unit 240. The control unit 240 isconnected to the gas supply valve 234 and a release valve 236. Thecontrol unit 240 in turn sends a signal 230 to the supply valve 234,which supply valve 234 opens to allow the high pressure gas to flow fromthe supply chamber 228 to the top portion 222 of the housing 221. Asensing device 242 measures the pressure P₂ inside the compensationchamber 222 and sends a signal to the control unit 240. The flow of thegas from the supply chamber 228 continues until the force 226 acting onthe anchor plate 223 equals the force 170 acting on the plunger 152 fromthe bottom in the compression chamber 160. In case, the pressure insidethe top portion of the housing 222 exceeds a point, wherein the force226 acting on the anchor plate 223 is more than the force 170 acting onthe plunger from the bottom, the release valve 236 receives a signal 232from the control unit 240 and opens to release a portion of the highpressure gas inside the top portion of the housing 222 so that theforces 226 and 170 becomes equal.

FIG. 13 illustrates yet another exemplary electromagnetic actuator 250including a pressure compensation system. The actuator 250 is housed inan exemplary housing 251. The housing 251 includes a bottom portion ofhousing 254 including the anchor plate 146, core 142, a bottom spring154 and a top spring 258 connected to the anchor plate 146. The force226 developed by the gas supplied by the supply chamber 228 acts on thetop spring 258 instead of directly acting on the anchor plate 146 asshown in FIG. 10. A piston 260 separating the top portion 252 and thebottom portion 254 of the housing 251 is connected to the top spring258. Operationally, once the gas is supplied to the top portion 252 fromthe gas supply chamber 258, the piston 260 moves towards the top spring258 to exert a force 226, which force 226 is controlled to be equal tothe force 170 acting on the plunger from the bottom. The advantage ofthis concept compared to the one of FIG. 12 is that the piston 260 staysmore or less in a fixed position, which reduces the dynamic load on thesealing of the piston 260. The dynamically changing force is provided bythe top spring 258, which can rapidly expand and compress according toits load. Additionally, the whole system of pressurized chamber and topspring can be designed to act as a damping component.

FIG. 14 illustrates an exemplary bi-directional actuator 270 configuredto obtain a failsafe position when electricity is turned off. The designof the actuator 270 is similar to that shown in FIG. 5 with additionalfeatures in the design of the top spring 274 and bottom spring 272 toachieve a fail-safe position when the electricity is turned off. For theunidirectional design, fail-safe position of the actuator is alwaysguarantied, because as soon as the electricity is turned off, the springpushes the anchor plate away from the core and the actuator achieves the“off” position. But in the bi-directional design as shown in FIG. 5,when electricity is turned off the anchor plate 86 may achieve anundefined position due to the presence of two cores with two sets ofcoils disposed within. Therefore it is very important to design thebi-directional actuators in such a manner that when the electricity isturned off, the actuator should be able to achieve an “off” positionautomatically.

In the exemplary actuator 270 as shown in FIG. 14, proper fail-safeposition can be achieved by adjustment of the stiffness of the firstspring or top spring 274 and the second spring or bottom spring 272. Theplot as shown in FIG. 14 shows the position of the anchor plate 86plotted along the horizontal “x” axis 282 against the force acting onthe springs along the vertical “y” axis 284. A line 286 shows thecharacteristics of the bottom spring 272 and another line 288 shows thecharacteristics of the top spring 274. When the electricity is turnedoff, in absence of any magnetic force, the only force acting on theactuator is the sum of the forces developed in the top and the bottomsprings 272 and 274 respectively. The slope of the curve 286 determinesthe stiffness of the bottom spring 272 and the slope of the curve 288determines the stiffness of the top spring 274. The sum of the forceswithin the actuator is obtained by adding the lines 286 and 288 toachieve a line 294. In the plot, line 292 represents a zero force lineas shown by the position 282 of the anchor plate. The line 294 meets thezero force line 292 in the plot at the point 298. The intersection point298 is achieved at a position of −1.1, which negative value in the “x”axis determines the position of the anchor plate at a position littlelower than the “o” position 282 and ensures a fail safe position of theactuator once the electricity is turned off.

FIGS. 15 and 16 show an exemplary actuator 300 similar to thebi-directional actuator 80 shown in FIG. 5 with an addition locksolenoid 312 configured to achieve the fail-safe position once theelectricity is turned off. The actuator 300 also includes a secondanchor plate 314 connected to the first spring 92. The lock solenoid 312is attached to two lock springs 316 and 318. FIG. 15 illustrates theactuator 300 in an “on” position, when the electricity is supplied tothe set of coils 96 and the anchor plate 86 is pulled towards the secondcore 84. Electricity from the same power source is supplied to the locksolenoid 312 and the lock spring 318 is pushed towards the lock solenoid312 thereby pushing the lock spring 316 in a compressed position.

FIG. 16 illustrates the exemplary actuator 300 when the electricity isturned off and the actuator 300 achieves a failsafe “off” position. Inoperation, when the electricity is turned off, the lock springs 316 and318 expand thereby pushing the anchor plate 86 towards the first core 82to achieve the failsafe “off” position.

FIGS. 17 and 18 illustrate exemplary actuators 320 and 330 ofunidirectional design as shown in FIG. 1 with additional permanentmagnets to develop a stronger magnetic force during actuation. As shownin FIG. 17, one or more permanent magnets 322 can be inserted intoactuator housing to reduce the current demand during the hold phase,wherein a significant amount of magnetic force is provided by thepermanent magnets. The exemplary actuator 320 as shown in FIG. 17, maydevelop high initial force at the beginning of the stroke as thepermanent magnet 322 are placed closer to the anchor plate 16. Howeveronce the anchor plate 16 is close to the core 14, more current will beneeded to keep the anchor plate 16 in the hold position (close to thecore 14) as the magnetic flux from the permanent magnets due to theirdifferent orientation do not contribute to hold the plunger 18 close tothe core 14. FIG. 18 shows another exemplary actuator 330, wherein oneor more permanent magnets 322 are disposed within the core 14 to enhancethe magnetic forces developed in the actuation process. In the exemplaryactuator 330, the permanent magnets 322 contribute to the magnetic fluxgenerated in the core 14 as the permanent magnets 322 are disposedwithin the core. Therefore, the initial force generated by this corewhen the coils 26 are energized are low due to the distance of theplunger 16 and the core 14. However at the end of the stroke, when theplunger 18 is close to the core 14, less current is needed (compared tothe embodiment shown in FIG. 17 to hold the plunger 16 close to the core14.

In all the actuators described, in operation, the velocity developed bythe plunger needs to be controlled without sacrificing the actuationspeed of the valves of the compressors. A higher impact velocity of theplunger may damage the actuator due to the force created by the impactvelocity at the end of the stroke. To reduce the impact velocity ofplunger, electrical, hydraulic, pneumatic or mechanical damping may beapplied. Proper mechanical damping can be achieved by inserting a pieceof material of high mechanical resistance into the kinetic path of theplunger. For electrical damping, the application of the current that issupplied to the solenoid for actuation of the valve may be controlled insuch a manner that a fast actuation is achieved with low impactvelocities.

FIG. 19 illustrates the reduction of impact velocity of the plunger bycontrolling the supply of current to the solenoid. As shown in FIG. 19,time is plotted in the horizontal axis 342 against the supply of currentin the vertical axis 344. Initially the current is supplied continuouslyas shown by the line 346 and close to the end of the stroke the currentis turned off for a duration of time (hereinafter noted as T_(off)) asshown by 348. The force acting on the plunger is plotted in the verticalaxis 352 against the horizontal time axis 354. The curve 350demonstrates the characteristic time development of the force on theplunger. This time interval T_(off) during which the current is switchedoff can reduce the impact velocity if the duration T_(off) as well asthe timing of this off-phase (t_(currentoff)) is chosen optimally.

The percent reduction of the impact velocity due to this electricaldamping method is plotted in the vertical axis 354 against the timing ofthe current shut off phase t_(currentoff) in the horizontal axis 352.Curves 360 and 362 illustrate the percent reduction in impact velocityfor the actuator with unidirectional design (as shown in FIG. 1) fordifferent duration of the current shut off phase T_(off). Curves 356 and358 illustrate the percent reduction in impact velocity for the actuatorwith bi-directional design (as shown in FIG. 5). These plots clearlyidentify an optimum time for the shut off phase t_(currentoff) for agiven shut off duration T_(off).

Various embodiments of this invention have been described in fulfillmentof the various needs that the invention meets. It should be recognizedthat these embodiments are merely illustrative of the principles ofvarious embodiments of the present invention. Numerous modifications andadaptations thereof will be apparent to those skilled in the art withoutdeparting from the spirit and scope of the present invention. Thus, itis intended that the present invention cover all suitable modificationsand variations as come within the scope of the appended claims and theirequivalents.

1. A valve comprising an electromagnetic actuator, said electro magneticactuator comprising: a solenoid comprising: at least one core; an anchorplate; and at least one coil disposed within said at least one core andconnected to a set of power electronics to supply current to said coils;a plunger connected to said anchor plate; at least one spring configuredto guide said plunger; and a pressure compensation system; whereinopening and closing of said valve is controlled by passing currentthrough said at least one coil.
 2. The valve of claim 1, wherein said atleast one core is an “E” shaped core or a “U” shaped core.
 3. The valveof claim 1, wherein said valve is used in a compressor.
 4. The valve ofclaim 3, wherein said valve is used as a suction valve in saidcompressor.
 5. The valve of claim 1, wherein said solenoid comprises afirst core and a first spring and a second core and a second spring andsaid anchor plate is disposed in between said first and second cores. 6.The valve of claim 5, wherein said solenoid is bi-directional.
 7. Thevalve of claim 1, wherein said pressure compensation system comprises apressure compensation chamber to balance a compressed gas force actingon said plunger.
 8. The valve of claim 7, wherein said pressurecompensation chamber is configured to hold a compressed gas from saidcompressor.
 9. The valve of claim 7, wherein said pressure compensationsystem comprises a first pressure compensation chamber in fluidcommunication with said compressed gas and a second pressurecompensation chamber in fluid communication with ambient air.
 10. Thevalve of claim 7, wherein said plunger comprises a hollow path in fluidcommunication with said compressed gas.
 11. The valve of claim 7,wherein said pressure compensation system comprises an electromechanicalcompensation system.
 12. The valve of claim 11, wherein saidelectromechanical compensation comprises a step motor to create a forceon said plunger.
 13. The valve of claim 7, further comprising a sensingdevice in fluid communication with said compressed gas and a set ofcontrol hardware and software.
 14. The valve of claim 7, wherein saidpressure compensation system comprises an external gas supply chamber influid communication with said pressure compensation chamber through agas supply valve and a pressure release valve in fluid communicationwith said pressure compensation chamber.
 15. The valve of claim 5,wherein said one of said first spring and second spring is configured toachieve a fail-safe position once the supply of said current isinterrupted.
 16. The valve of claim 5, wherein one of said first springand second spring is connected to a lock solenoid and a third spring toachieve a fail-safe position once the supply of said current isinterrupted.
 17. The valve of claim 1, wherein said actuator furthercomprises one or more permanent magnet.
 18. The valve of claim 1,wherein an electrical damping method is used to control the impactvelocity of said plunger.
 19. The valve of claim 1, wherein said atleast one core comprises iron.
 20. A valve comprising an electromagneticactuator, said electro magnetic actuator comprising: a solenoidcomprising: at least one core, said at least one core is an “E” shapedcore or a “U” shaped core; an anchor plate; and at least one coildisposed within said at least one core and connected to a set of powerelectronics to supply current to said coils; a plunger connected to saidanchor plate; at least one spring configured to guide said plunger; anda pressure compensation system wherein said pressure compensation systemcomprises a pressure compensation chamber to balance a compressed gasforce acting on said plunger; wherein opening and closing of said valveis controlled by passing current through said at least one coil and saidvalve is used in a compressor.
 21. The valve of claim 20, wherein saidpressure compensation chamber is configured to hold a compressed gasfrom said compressor.